This invention relates generally to process instruments used in industrial process control systems. More particularly, the present invention relates to process transmitters having mechanical integrity verification. Automated mechanical integrity verification is defined as the ability of a device to self validate its own mechanical construction or assembly. It includes verification that components are properly installed (such as tightness of electronic housing covers), verification that components are the proper material (such as wetted flange material), and verification that components are properly oriented (such as housing rotation).
Process transmitters are used to remotely monitor process variables, such as pressure, temperature or flow, of process fluids, such as petrochemicals or water. A process transmitter typically includes a sensor or transducer that produces an electrical output in response to physical changes in a process variable. For example, capacitive pressure transducers or piezoresistive pressure transducers produce an electrical signal as a function of the pressure of a process fluid. The electrical signal of the sensor is processed by the transmitter circuitry to produce an electrical output that can be monitored as an indication of the pressure of the process fluid. A process transmitter also includes electronics for either remotely monitoring the electrical output through a control loop or network at a central monitoring location such as a control room, or locally such as with an LCD screen.
In order to couple these electrical components with the process fluid, the components are contained in a housing that can be mounted to a process fluid vessel, such as a storage tank or pipeline, with process wetted components such as flanges, manifolds, diaphragms or other transmitter mounting components. It is critical that the housing and the process wetted components be properly selected and assembled for the desired application. For example, in order to survive contact with harsh or hazardous process fluids, the process wetted components must be composed of a suitable material. If improper materials are used the components could corrode, degrade and eventually fail, thus producing inaccurate results or altogether failing to function. Once the proper components are selected they need to be properly assembled to ensure functional and mechanical integrity. Improperly assembled mounting components could result in inaccurate results and safety hazards. For example, improperly seated covers on process transmitter housings may prevent the crucial flame-quenching threading from containing sparks, or tiny explosions therefrom, from spreading to the outside environment. Additionally, improperly threaded covers allow moisture or other contaminants into the process transmitter housing. Process flanges of differing materials and properties look similar and can be difficult to visually distinguish. Due to the risks involved, it is not adequate to rely on transient solutions such as labels to prevent the installation of improper components. Likewise, covers that are not fully threaded are difficult to detect and visual inspection cannot be fully relied upon. Therefore, there is a need for improved means of verifying that process transmitters are properly assembled.